The present invention relates to a ceramic porous body usable as a filter capable of filtering fluids such as liquids, gases and the like.
Ceramic filters are used for water treatment, exhaust gas treatment, and the removal of floating substances, bacteria, dusts, etc. in liquids and gases in various fields inclusive of medicine and foodstuff industries, since they have excellent physical strength, durability and corrosion resistance.
A ceramic porous body used for a ceramic filter as a substrate, a filtration membrane or an intermediate membrane for forming a filtration membrane, is formed by directly sintering ceramic particles, firing ceramic particles after adding a sintering aid to the ceramic particles, and firing the ceramic particles which are bonded with a vitreous binder, or the like. As an example of a glass fit desirable for a binder of this kind of porous body, there is proposed in JP-B-6-67460 a glass frit which is a compound mixture of a borosilicate and an alkaline flux with rare earth metal oxides and contains zirconia in a high level.
In the case that when a ceramic porous body is used, for example, in a filtration filter for water purification, it is periodically required to subject the ceramic porous body to chemical cleaning to remove clogs. Such cleaning is typically performed by decomposing organic substances with an alkaline sodium hypochloride solution, and treating inorganic substances with an acidic citric acid solution. Thus, in this cleaning, the ceramic porous body is alternately exposed to acid and alkali, and, thus, corrosion resistance against both acids and alkalis is required for a binder of the ceramic porous body.
However, the glass frit described in JP-B-6-67460 is poor in alkali resistance since it contains B2O3. Furthermore, in general, borosilicate glasses including the above glass frit have low resistance against at least either of acids and alkalis.
Therefore, ceramic porous bodies in which a conventional glass frit is used as a binder could not be used as filtration filters for a long period under circumstances where ceramic porous bodies are exposed to acid treatment and alkali treatment, repeatedly.